Add column headers to dataframe

[volcano63]

OK, here is a simple example how to use apply in your code

url_template = "http://api.wunderground.com/api/88fb15b49e765a43/conditions/q/{state}/{city}.json"
def get_weather(row, *fileds):
    url = requests.get(url_template.format(state=row['State'],city=row['City']))
    observation = url.json()['current_observation']
    
    return [observation[field] for field in fields]

fields = ['temp_f', 'relative_humidity']
stadiums = pd.DataFrame([['SFG', 'CA', 'San Francisco'], ['NYY', 'NY', 'Bronx']], 
                        columns=['Team', 'State', 'City'])
print(stadiums.apply(lambda r: get_weather(r, *fields), axis=1).values)

And the result is

Output:
[list([54.7, '82%']) list([63.0, '83%'])]

now,

stadium[fields] = pd.DataFrame(<result>)

will update your stadiums DataFrame with new fields - but you have to convert the result to a form accepted by pandas.DataFrame constructor. I will let you experiment with that on your own.

PS pandas is an amazing tool which I just started learning myself - but you have to understand, DataFrame and Series are objects intended for processing as a whole - otherwise, you abuse pandas. Learn it properly